Renal scanning composition and method using technetium 99m

ABSTRACT

A scintillation type renal scanning agent comprising reduced technetium 99m, penicillamine and acetazolamide (DIAMOX).

United States Patent Halpern et a1.

[451 July 31,1973

RENAL SCANNING COMPOSITION AND METHOD USING TECHNETIUM 99M Inventors: Samuel E. Halpern, San Diego;

Manuel Tubis; John S. Endow, Los Angeles, both of Calif.

Appl. No.: 156,567

Assignee:

US. Cl 250/7l.55, 252/301.1 R, 424/1 Int. Cl G0lt 1/20, A61k 27/04 Field of Search 424/1; 250/106 T,

[56] Reierences Cited UNITED STATES PATENTS 3,436,354 4/1969 Gemmill 252/301.1 R 3,466,361 9/1969 Richards 424/1 Primary Examiner- Benjamin R. Padgett Attorney-John S. Roberts, .lr., Norman J. Latker et a1,

[57] ABSTRACT A scintillation type renal scanning agent comprising reduced technetium 99m, penicillamine and acetazolamide (DIAMOX).

4 Claims, No Drawings The present invention relates to an improved renal scanning agent of the scintillating type using a radioisotope. The present composition embodies a kidney scanning agent with technetium 99111 as the active scintillating agent complexed or chelated with penicillamine and also containing as a carrier acetazolamide (DIA- MOX). The function of the penicillamine is to keep the technetium 99m in a reduced state and to exclude the Tc(+7) pertechnetate variety.

Scintillation scanning or radioisotope scanning is well known in the art and in the laboratory, viz.:

David Sutton, Textbook of Radiology (1969), E. S.

Livingstone (London), pp. 955-956. Wang, Yen, Clinical Radioisotope Scanner (1967),

C. C. Thomas, pp. 170-198 The use of radioactive agents for renal scanning has developed rapidly since about 1960. One agent proposed and utilized is l3l-Iodine Hippuran or l-labeled ortho-iodo hippurate. l-laynie, T. P., et al., Clin. Research 8, 288 (1960).

Mercurial compounds as illustrated by Hg 203 Chlormerodrin (Neohydrin Lakeside), McAfee et al., Radiology, 75, 820-821 (1960) have also been utilized. Again, observers have noted deficiencies in the regimen involved due to unacceptable radiation dosage to the patient or poor tissue penetration.

lndium 1 13m DTPA (diethylene triamine penta acetic acid) Complex has also been utilized but this compound introduces difficulties of operation with optimum scintillation camera equipment.

Of greater relevance to the present invention are two 99m Technetium labeled compounds or complexes that have been used for renal scanning. The first is 99m Technetium DTPA (diethylene triamine penta acetic acid) described in U.S. Pat. No. 3,466,361, Richards et al (U.S.A.). The DTP A chelates generally as sequestering agents are described in U.S. Pat. No. 3,150,160, Dexter (Geigy). The action of this complex has been found to depend entirely on glomerular filtration and scan quality goes down when the filtration rate decreases.

A second Technetium compound or complex which has been utilized is 99m Technetium-lron-Ascorbic acid complex. In use, this complex has a high liver background which degrades the scan if serum creatinines exceed 3.0 mg%.

ln an effort to meet the objections of investigators to prior art compounds noted above, the radiopharmaceutical of the present invention comprises a ternary composition of Technetium-99m, acetazolamide and penicillamine.

TECHNETIUM 99M The selection of this particular radioisotope was engendered by its excellent physical characteristics. The six hour half-life and absence of beta radiation makes feasible the administration of millicurie amounts of the nuclide. Its gamma emission of 140 KeV has satisfactory tissue penetration and yet is readily collimated. The preferred species utilized for the composition is carrier-free TcO, Tc 99m which is abbreviated in this application to mean and to be Tc99m. As utilized, the Tc99m has a very small mass of the order of micromolat amounts as 1.9 X 10- nM and thus can be designated in a composition as a tracer amount.

ACETAZOLAMIDE (DIAMOX) This compound (U.S. Pat. No. 2,554,816, Clapp et al., American Cyanamid, and U.S. Pat. No. 2,980,679, Omikron-Gagliardi Soc. Fatto) is utilized to be associated with the Tc99m so that the composite is excreted from the body by tubular secretion. This action of acetazolamide in the kidney is described in Goodman and Gilman, The Pharmacological Basis of Therapeutics, 4 (1970), pp. 851-854, Macmillan.

D-PENICILLAMINE (B-MERCAPTO VALINE) This compound occurs in nature as a natural product of degradation of penicillins. Its function in the present invention is to reduce the TcO 'Tc 99m metal" and exclude the higher valence form such as +7. This unde' sired variety is known as pertechnetate. Metal complexes with penicillamine are known and have been described in the literature, viz., D. A. Doombos et a1, Pharm. Weekblad 99, 289 (1964). In the present milieu, it has been found that in acid environment the pertechnetate is rapidly reduced in the presence of D- penicillamine and does not revert to pertechnetate. The results were superior to other routes tried and also superior to the known ascorbic acid method which gave a broad spectrum of rapidly changing valence states. The method of the present invention permits the reduction of the Tc99m Pertechnetate to a single stable valence, making labeling more efficient.

MOLAR COMPOSITION With respect to the composition of the product the optimum component molar values are about:

Acetazolamide TcO, 99m: D-Penicillamine:

UTILITY MODUS By analogy with the chelate of the closely related VIIB metal manganese, it is believed that technetium chelates with D-penicillamine through the sulfur and nitrogen atoms. Also, the indications are that a part of the D-penicillamine is used to reduce the pertechnetate to a lower valence which then chelates with penicillamine. It is further postulated that additional chelation or complexing occurs with acetazol-amide, which is 5- acetamido-1,3,4 thiadiazole-Z-sulfonamide, and has nitrogen and sulfur atoms with potential chelating properties for the available metal.

Standard tests have shown that the TPAC is 99 percent protein-bound regardless of the modality used in testing. The majority of TPAC appears associated with the albumin fraction. Autoradiographs of the kidneys show a great majority to be concentrated in the renal cortex and histological studies indicate that the mechanism of extraction is not glomerular and apparently the 3 entire complex or a part thereof is extracted from the plasma by the kidneys.

EXAMPLE l PREPARATlON OF TPAC: 99M TC-PENlClLLAMiNE-ACETAZOLAMIDE COMPLEX To 4.0 ml of 0.9% NaCl solution of sodium pertechnetate (Tc99m) in a sterile, pyrogen-free 15 ml. centrifuge tube was added 60 mg. (0.40mM) of D- Penicillamine, 1.0 ml. of concentrated (11.6N) hydrochloric acid and 400 mg. (0.18mM) of acetazolamide (DIAMOX Lederle Labs). The solution was shaken and the pH of the mixture was adjusted to 8.5 to 8.7 with aqueous concentrated sodium hydroxide. The pH value is critical and should be between 8.5 and 8.7, but definitely not higher due to decomposition of the acetazolamide above pH 8.7.

The mixture was then autoclaved for 15 minutes at l5 lbs. pressure. After cooling the mixture by running tap water over the centrifuge tube, the solution was filtered through a 0.22M Millipote filter into a sterile pyrogen free vial.

Samples were taken for sterility and pyrogen tests. The final solution was assayed for its radioactivity. lts purity and identity were established by paper chromatography.

EXAMPLE ll EXAMPLE OF USE (l.E., DISTRIBUTION) OF THE COMPLEX IS:

at. Animal White Mice After initial injection of the TPAC, the greatest count on a per milligram basis was in the liver. However, after l5-30 minutes the Tc99m isotope accumulates almost completely in the kidney. Very little activity was found in either the urine or normal brain tissue Excellent scans were obtained after -30 minutes The mice studies also indicated that the half-time disappearance from the blood is about 60 minutes. Further, the lower counts in liver on a per milligram basis are about the same as those of blood indicating that the Qt liver is not storing the radiopharmaccutical. b. Rabbits Eight rabbits were injected with the TPAC and the relative distribution of the radioactivity was the same as that found in the mice. Some rabbits were given multiple injections to test for adverse effects on the kidneys, but none were found.

c. Dogs Two dogs were injected with the TPAC and a similar distribution of radioactivity as stated above was found, using scintiphotography. 'l he dogs suffered no adverse reactions over the two-month period in which they were studied.

In all cases of the three examples, the scans were of high quality and remained unchanged from study to study. Formal clearance studies using inulin as a base line showed the clearance rate of the 99m TcPenicillamine-Acetazolamide Complex was only 1 percent that of the inulin indicating that what enters the kidney is only sli htly excreted in the urine.

We claim;

1. A method of scintillation scanning in mammals which comprises injecting i.v. in said mammals a sterile composition having a pH value of about 8.5-8.7 consisting of technetium 99m, penicillamine and acetazolamide, allowing the composition to collect in the renal cortex and after a post injection time interval of 13-45 minutes, scintigraphically recording the results by scanning.

2. A method according to claim 1 wherein the postinjection time interval is about 30 minutes.

3. A composition suitable for kidney scintillation scanning consisting of reduced technetium 99m (Tc99m), penicillamine and acetazolamide wherein penicillamine and acetazolamide are in the molar ratio of about 2:] and the Tc99m is in tracer, carrier-free amounts.

4. A composition according to claim 3 wherein penicillamine and acetazolamide are in the molar ratio of about 2.0209 and the Tc99m is in tracer, carrier-free amounts.

* k a e 

2. A method according to claim 1 wherein the post-injection time interval is about 30 minutes.
 3. A composition suitable for kidney scintillation scanning consisting of reduced technetium 99m (Tc99m), penicillamine and acetazolamide wherein penicillamine and acetazolamide are in the molar ratio of about 2:1 and the Tc99m is in tracer, carrier-free amounts.
 4. A composition according to claim 3 wherein penicillamine and acetazolamide are in the molar ratio of about 2.0:0.9 and the Tc99m is in tracer, carrier-free amounts. 